Geographic distribution of Gryllotalpa stepposa in south-eastern Europe, with first records for Romania, Hungary and Serbia (Insecta, Orthoptera, Gryllotalpidae)

Abstract Described from the steppe zones north of the Black Sea, Caucasus, and central Asia, Gryllotalpa stepposa Zhantiev was recently recorded from a few localities in Greece, R. Macedonia, and Bulgaria. In May 2015, several specimens were collected from Ivrinezu Mare in Romania, which suggested a continuous distribution area of the species, stretching from the central Balkans to central Asia. Thus, to reveal its actual range of occurrence, a survey of several Orthoptera collections became mandatory and, as expected, a large number of misidentified specimens of Gryllotalpa stepposa were discovered, providing new data on the species distribution in south-eastern Europe, including also the first records of this mole cricket in Serbia and Hungary. Here a full locality list is presented of this species west of Ukraine and Moldova and the current geographic distribution of the genus Gryllotalpa in the Balkans is revised. A key for distinguishing the mole crickets in south-eastern Europe and a distribution map for this region are presented.


Introduction
Although the Orthoptera fauna of south-eastern Europe, including the Balkan Peninsula, is comparatively well explored, several faunistic and taxonomic issues remain and most of these address one of the most fragmentary known groups: the crickets. In the past decades, during the extensive work of exploring the Orthoptera fauna in this area, Tettigonioids and Acridoids received the highest attention, while the Grylloids were neglected, most likely due to their elusive, nocturnal way of life.
The mole crickets form a particular group within the Grylloidea. Family Gryllotalpidae includes eight genera with more than 100 species, excluding the fossil/extinct ones (Eades et al. 2016). These insects are adapted to living underground, having reduced ovipositor, fore legs highly modified for digging and hind legs fully losing their jumping ability during the ontogenesis (e.g., Gorochov 1995).
Gryllotalpa Latreille is a subcosmopolitan genus, missing only from the northernmost areas of Asia, whole south America and the boreal areas of north America. The Gryllotalpa gryllotalpa species group occurs throughout Europe, from Britain to Iran and central Asia (Gorochov 1993;Broza et al. 1998;Ingrisch et al. 2006). Fifteen species are known within the Gryllotalpa gryllotalpa group, out of which 12 are found in Europe: G. gryllotalpa (Linnaeus, 1758) -present all over Europe, excepting the southernmost areas; G. septemdecimchromosomica Ortiz, 1958 -present in the Iberian Peninsula, southern France, Tuscany and Umbria in Italy; G. vinae Bennet-Clark, 1970 -in southern France; G. sedecim Baccetti &Capra, 1978 andG. octodecim Baccetti &Capra, 1978 -in north-western Italy, south-eastern France andSardinia;G. quindecim Baccetti &Capra, 1978 -in south Italy andSicily, G. viginti Baccetti &Capra, 1978 -in north-western Italy (Liguria); G. cossyrensis Baccetti & Capra, 1978in Pantelleria island;G. vigintiunum Baccetti, 1991 -in Sardinia;G. krimbasi Baccetti, 1992 -in Greece;G. stepposa Zhantiev, 1991 -in the Balkan Peninsula, Moldova, south Ukraine, the southern part of the steppic zone of European Russia, the Caucasus, central Asia, Saudi Arabia; and G. unispina Saussure, 1874 -along the coasts of the Black and Caspian Sea and in central Asia (Bacetti and Capra 1978, Zhantiev 1991, Broza et al. 1998, Ingrisch 2006. The mole crickets excavate two different types of tunnels: vertical burrows, used for hiding from predators, overwintering and molting, and horizontal tunnels for feeding, mating and escaping predators (Jafari et al. 2015). Males stridulate in the evening and at night from a special acoustic chamber, usually cylindrical, with one to several openings extended upward; five types of song are known: calling, precopulation/courtship, territorial, aggressive, and remonstrative (Zhantiev et al. 2003). In some species, the females also sing with a secondarily developed stridulatory apparatus on the upper side of some tegminal veins (Ragge and Reynolds 1998). In the genus Gryllotalpa, both oscillographic analysis and song frequency can be used when separating species, e.g. Gryllotalpa gryllotalpa and G. vineae (Ragge and Reynolds 1998); G. gryllotalpa, G. unispina and G. stepposa (Zhantiev et al. 2003); G. tali Broza, Blondheim & Nevo and G. marismortui Broza, Blondheim & Nevo (Broza et al. 1998). Other characters used in species discrimination are: male genitalia, wing venation, number of teeth in the stridulatory file, morphometrics, number of chromosomes and even cuticular hydrocarbons (Broza et al. 1998;Ingrisch et al. 2006).
In the present paper light is shed on the distribution of Gryllotalpa species in south-eastern Europe, based on extensive material from this area. Recent data revealed that four species of Gryllotalpa occur in south-eastern Europe and the Balkan Peninsula: G. gryllotalpa, G. stepposa, G. unispina and G. krimbasi. In order to distinguish these, several morphological traits are used and included in a key.

Materials and methods
Gryllotalpa specimens were found while actively searching in moist ground, preferably near a water source. The easiest and most efficient way was the collection of specimens attracted to black Ultra Violet fluorescent tubes and Mercury vapor light lamps. The material preserved in the following collections was revised:

MGAB
"Grigore Antipa" National Museum of Natural  (Chobanov and Mihajlova 2010). A database with all the studied material is available as a Suppl. material 1. Specimens were identified according to the general and genital morphology, venation of tegmina and structure of the stridulatory file. Distribution of chromosomal forms (number of chromosomes in the karyotype of certain populations) from earlier published sources was also taken into account (compare References).
Photos used in the key were taken with a Canon EOS 6D DSLR camera and a Canon MP-E 65 mm lens. For genitalia microphotographs, the camera was mounted to a Leica 205C Stereomicroscope.

Key for the identification of south-east European species of Gryllotalpa:
1 Space between the proximal and next dorsal inner spine on hind tibiae wide, larger than the space between the distal spines (Fig. 1A). Tegmina with weak light-colored veins (Fig. 1D). Apical part of epiphallus shovel-like widened; its tip usually convex and flattened (Fig. 1I) 1B, C). Tegmina with strong dark-colored veins (Fig. 1E, F). Apical part of epiphallus widened or not but the tip concave, dorso-ventrally thick and humped, forming a longitudinal ventral slot (Fig. 1J, K)  Epiphallus short and wide (less than 2× longer than its widest part), apically more flattened, with a shallow ventral slot (Fig. 1K). Distal part of the median vein (♂) opposite to the radial branch 1 (transverse radio-cubital vein) weak and poorly visible (Fig. 1H)

Discussion
Until recently only Gryllotalpa gryllotalpa, G. unispina, and G. krimbasi were known to occur in the Balkans. The latter was recently described from Greece (Baccetti 1992) following the results by Krimbas (1956;1960) and relying on a male karyotype with 19 chromosomes, but without giving any structural characteristics and even using a nymph as a holotype. This chromosome number corresponds to the male karyotype of Gryllotalpa unispina. Later on, Ingrisch et al. (2006) redescribed Gryllotalpa krimbasi using specimens from the distribution range of the 19-chromosome form (central Greece). According to new material observed, Gryllotalpa krimbasi is hardly distinguishable morphologically from G. stepposa using both general morphology and the male phallic complex. The differences in the ratio length: width of epiphallus (proposed by Ingrisch et al. 2006, using the drawings of Gryllotalpa stepposa by Zhantiev 1991) are considered unreliable after measurements implemented for this study, due to a clear overlap. On the other hand, Gryllotalpa krimbasi (as well as G. stepposa) differs well from G. unispina in the shape of male genitalia, body shape, number of spines on the hind tibia etc. Both species differ also in their habitat preferences. While Gryllotalpa unispina is a halophilous species distributed along the northern and eastern Black Sea coast, surroundings of the Caspian Sea, central and south-western Asia (Zhantiev 1991;Gorochov 1993), G. krimbasi prefers inland humid habitats and seemingly avoids saltings. In 1939, Steopoe, following the works of Voinov (1912), shows that a "14 chromosomes form" with variations of 15 and 16 chromosomes is present in Romania and named it "Romanian form". He points out the differences of the metaphasic chromosomes between the so called Romanian form, the typical form of Gryllotalpa gryllotalpa (2n=12) and the "Naples form" with 15 chromosomes. According to Zhantiev (1991), G. stepposa also has a karyotype with 14 chromosomes (and occasionally 15 or 16) and such forms were found in southern Turkey (Kushnir 1956), on the Greek mainland and some Aegean Islands (e.g., Krimbas 1956;data in Willemse 1984). Recently, morphological examination revealed that the typical Gryllotalpa stepposa occurs in the Republic of Macedonia (Chobanov and Mihajlova 2010) and Bulgaria (Chobanov 2009; 2011). With the current study we prove that the range of this species is significantly wider, covering Romania (thus making the connection with the range of the species in Moldova and Ukraine), all the territory of Bulgaria and eastern Macedonia (as high as 1000-1200 m asl), north-eastern Greece (on the territory of the district of east Macedonia and Thrace), the lowland of northern (possibly also central and south) Serbia, and some areas of Hungary (Figure 1). Its occurrence in eastern Croatia and partly in Bosnia and Herzegovina is expected, and even its discovery in Slovakia and eastern Austria would not be surprising.
With the present data, Gryllotalpa stepposa almost entirely replaces G. gryllotalpa on the Balkan Peninsula. In the south and west, Gryllotalpa stepposa borders G. krimbasi in Greece: the ranges of both species border approximately in the lower courses of Vardar (Axios) or Strouma (Strimon) rivers. Thus, both taxa are possibly direct competitors and exclude each other. The western border of the range of Gryllotalpa stepposa is unclear for the moment. In the north (Croatia, Serbia, Hungary, and north Romania), Gryllotalpa stepposa meets G. gryllotalpa (compare map in Baccetti and Capra 1978), thus the taxonomic identity of all published G. gryllotalpa data from this region is uncertain. The patchy and scarce distribution of Gryllotalpa gryllotalpa in Bulgaria (only a single locality known close to the border with Serbia) and Republic of Macedonia (two isolated localities in the south) suggests recent expansion of G. stepposa in the west and north and replacement of G. gryllotalpa, whose current occurrences may represent remnants from a former wider range. In the valley of Drin River and the connected plain of Ohrid Lake (extreme south-western Macedonia), only Gryllotalpa gryllotalpa was found; thus, this area may represent the southernmost border of its population, linking its range in northern Italy and central Europe through the northern Adriatic coast.